Papers by Keyword: Photoluminescence (PL)

Abstract: In this study, We demonstrate mono and few layers MoS₂ samples on the SiO₂(270nm)/Si substrate from bulk MoS₂ crystal by micromechanical exfoliation technique. We have systematically studied Atomic Force Microscopy, Raman and PL properties of mono and few layer MoS₂ on the SiO₂(270nm)/Si substrate. First, we find that the number of layer values dependent the Raman and PL emission. First, Raman intensity area ratio of the MoS₂ E¹_2g, A_1g and 2LA modes to that area of the Si substrate increased linear with increasing number of layers MoS₂. Second, Normalized PL intensity area of the (A) peak decreased linear with increasing number of layers MoS₂. The value of those graphs is a method to understand the number of layers the exfoliated MoS₂.

Abstract: Many trivalent rare earth ions such as Er³⁺, Tm³⁺, Ho³⁺, Pr³⁺ and Nd³⁺ were doped as absorption and emission centers in glass hosts. In this work, lead borotellurite (PBT) glass doped with neodymium ion (Nd³⁺) has been prepared and characterized by mean of their optical properties. The UV-Vis measurement has been carried out in order to determine the optical band gap energy, reflective indices and the polarizability. Optical absorption spectra of the glass samples are recorded in the range 400–900 nm at room temperature From the result, there are six significant absorption peaks that corresponds to 525 nm, 584 nm, 683 nm, 747 nm, 805 nm and 878 nm wavelength have been observed with the most predominant peak to be used as excitation wavelength is found centered at 584 nm. The energy band gaps as well as the refractive indices were found to vary from 2.50eV to 2.59eV and from 1.89 to 1.96 with mol% of Nd content respectively. Meanwhile, the polarizability shows a similar trend of results to refractive indices as it varies from 5.56 x 10^-24 cm³ to 5.63 x 10^-24 cm³. These results will be discussed further in details.

Abstract: Achieving tuneable photoluminescence via controlled co-doping of rare earth ions in lithium niobate based glasses are challenging. A series of Er³⁺/ Nd³⁺ co-doped tellurite glasses of composition (70-x-y) TeO₂ – 15 Li₂CO₃ – 15 Nb₂O₅ – (x) Er₂O₃ – (y) Nd₂O₃ with x = 0; 1.0 mol % and 0 ≤ y ≤ 1.0 mol % are prepared using melt quenching technique. The influence of co-dopants on the emission properties is analyzed and discussed using partial energy level diagram of rare earth ions. The dopants concentration dependent physical properties such as refractive index, molar volume, density, polarizability and molar refractions are determined. The down-converted luminescence spectra for ²G_9/2 à⁴I_9/2 transition reveal a strong green emission band centred at 497 nm is attributed to the energy transfer from erbium to neodymium ion. The emission spectra exhibit five prominent peaks centred at 497, 539, 553, 616 and 634 nm corresponding to the transitions from ²H_11/2, ⁴S_3/2 and ⁴F_9/2 excited states to the ground state of Er³⁺ ion and the transitions from ²G_9/2, ²G_7/2, ²H_11/2 and ⁴F_9/2 excited states to ground state of Nd³⁺ ion. The highest intensity is achieved for x = y = 1.0 mol%. The excellent luminescence response suggests that our glasses may be nominated for solid state lasers and other photonic applications.

Abstract: Porous silicon (PS) was successfully synthesized via novel integrated pulsed electrochemical etching of an n-type (100) silicon (Si) substrate under various condition. The PS was etched using hydrofluoric acid (HF) based solution and the porosity was optimized by introducing electroless chemical etching process prior to photo electrochemical (PEC) anodization. In the electroless etching, a delay time (T_D) of 2 min was applied. After that a cycle time (T) and pause time () of pulsed current were supplied throughout the 30 min PEC etching process. As grown Si and PS through conventional direct current (DC) anodization were also included for comparison. The result obtained showed that applying delay time helps to improve the uniformity and density of the porous structures. AFM indicated that the roughness of the Si increases as the dissolution of the Si occurred. Raman spectroscopy showed that an improvement in the crystalline quality of PS under pulse etching method compared to DC method indicated by the reduction of full width at half maximum (FWHM). A broad visible photoluminescence (PL) was observed from green to red with blue shift as nanocrystallite size decreases which constituted quantum confinement effect from the PS structures. Nickel (Ni) finger contact was deposited onto the PS to form metal semiconductor metal (MSM) photodetector. Ni/PS MSM photodetector by pulse method exhibited higher gain (2 times) compared to conventional Si device at 5 V bias.

Abstract: Porous GaN structures were formed from crystalline GaN on conducting AL₂O₃ substrate using Pt-assisted electroless etching in HF: CH₃OH: H₂O₂ = 1:4:4 under illumination of 500 W UV lamp. Scanning electron microscope (SEM) photoluminescence (PL) and Raman spectra measurements evidenced important features of the pore morphology, nanostructures and optical properties. According to the SEM micrographs, the three-dimensional ridge structure appears with the formation of porous material between the ridges. The porous layer exhibited a substantial PL intensity enhancement with red-shifted band-edge PL peaks associated with the relaxation of compressive stress. The shift of E₂(high) to the lower frequency in Raman spectra of the porous GaN films further confirms such a stress relaxation.

Abstract: The formation of nanocrystalline porous silicon (PS) was successfully prepared under a novel alternating current (sine-wave a.c. (50 Hz)) photo-assisted electrochemical (ACPEC) etching condition of an n-type (100) silicon (Si) substrate under the illumination of an incandescent white light. As grown Si and PS through conventional direct current(DC) anodization were also included for comparison. The ACPEC formed porous Silicon (PS) with excellent structural and surface morphological characteristic. According to the field emission scanning electron microscope (FESEM) micrographs, the nanoporous structures exhibited pores with uniform circular structure with estimated sizes, ranging between 20.5 nm and 30.5 nm. The atomic force microscopy (AFM) revealed an increase in the surface roughness induced by porosification. As compared to the as-grown Si, PS by AC method exhibited a substantial visible photoluminescence (PL) intensity enhancement with blue-shift associated with the quantum confinement effect of the nanostructure Si. Thermally treated nickel (Ni) finger contact was deposited on the PS to form MSM photodetector. Ni/PS MSM photodetector showed lower dark and higher photocurrent compared to the as grown Si device.

Abstract: This paper is devoted to the consideration of currently available studies on obtaining stimulated infrared emission in structures based on HgCdTe quantum wells. Also analysis and interpretation of discussed experimental results are presented in this article.

Abstract: Eu³⁺-doped lithium barium borate glasses of the composition 50Li₂O : 20BaO : (30-x)B₂O₃ : xEu₂O₃, where x = 0.00, 0.10, 0.30, 0.50, and 1.00 mol%. The glasses were fabricated by normal melt quenching technique at 1,000^°C and their properties were investigated. The emission spectra of Eu³⁺-doped glasses were recorded in wavelength range of 550-770 nm with 394 nm excitation. All the spectra exhibited 5 emission bands corresponding to the ⁵D₀→⁷F₀, ⁵D₀→⁷F₁, ⁵D₀→⁷F_2, ⁵D₀→⁷F₃ and ⁵D₀→⁷F₄ transition, respectively. The peak intensities increase with the increase of concentration from 0.10 to 1.0 mol%

Abstract: Dysprosium doped lithium lanthanum borate glasses (LiLaB:Dy³⁺) were prepared by the melt quenching technique, varying the Dy₂O₃ doped concentration from 0.00 to 1.50 mol%. The absorption spectra showed that LiLaB:Dy³⁺ glass absorbed photon in visible light and near infrared region. From the excitation of 388 nm, this glass emitted the photon with 483, 575, 664 and 753 nm wavelength. The intensity of emission increased with increasing of Dy₂O₃ concentration until 1.0 mol%, after that it decreased. The Judd-Ofelt (J-O) analysis was applied to 1.0 mol% doped glass to investigate the J-O parameter, radiative transition possibility and stimulated emission cross section. These values were interpreted to the ability of laser gain medium.

Abstract: The photoluminescence properties of lithium yttrium borate glasses doped with Eu³⁺ (LiYB:Eu³⁺) were studied in this work. Glass samples were prepared by melt-quenching technique with variation of Eu₂O₃ doped concentration between 0.00 – 6.00 mol%. The absorption spectra show that LiYB:Eu³⁺ glasses absorbed photon in visible light (VIS) and near-infrared (NIR) region. Photon absorption at 394 nm can excite glass to emit the number of photons in VIS region such as 591, 613, 653 and 701 nm. The strongest emission belong to the light with 613 nm wavelength. The optimum concentration of Eu₂O₃ for LiYB glass is 4.00 mol%. Judd-Oflet (J-O) analysis was used to study on 4.00 mol% doped glass, which shows the interesting potential for using this glass as gain medium in 701 nm emitting laser.